python __slots__ Slots are a mechanism that allow you to declare class attributes - Python__ dict __ slots is a Python class feature Mastering Python `__slots__`: Optimize Memory and Performance

Pythondataclass In the world of Python programming, efficiency is often a key consideration使用__slots__ - Python教程- 廖雪峰的官方网站. When dealing with a large number of objects, the memory footprint can become a significant factor. This is where the `__slots__` mechanism in Python comes into play, offering a powerful way to optimize class instances. By understanding and effectively utilizing `python __slots__`, developers can significantly reduce memory consumption and potentially accelerate program execution.

What are `__slots__`?

At its core, `__slots__` is a special class attribute that allows you to explicitly declare data members for instances of a class.Using Slots in Python Unlike regular Python classes, which dynamically create a `__dict__` attribute for each instance to store its attributes, classes defined with `__slots__` forgo this `__dict__`. Instead, Python reserves a fixed amount of space in memory for the attributes that are specified within the `__slots__` definition.Python Trick: The Magic of __slots__

The `__slots__` attribute itself must be defined as a sequence, typically a tuple of strings, where each string represents an allowed attribute name__slots__ are implemented at the class levelby creating descriptors (3.3.2) for each variable name. As a result, class attributes cannot be used to set .... This declaration must be present at the time the class is defined.__slots__ is an attribute you can add to a Python classwhen defining it. You define slots with the possible attributes that an instance of an object can ... For instance, to define a `Dog` class with `name` and `breed` attributes, you would write:

```python

class Dog:

__slots__ = ('name', 'breed')

def __init__(self, name, breed):

self.name = name

self.breed = breed

```

When you declare `__slots__`, it restricts the valid set of attribute names on an object to precisely those listed__slots__ conflicts with class variable - Python Help .... Any attempt to assign an attribute not defined in `__slots__` will result in an `AttributeError`The __slots__ declarationallows us to explicitly declare data members, causes Python to reserve space for them in memory, and prevents the creation of __dict__ ....

Benefits of Using `__slots__`

The primary advantages of employing `__slots__` revolve around memory optimization and performance gains.

Memory Efficiency

The most prominent benefit of `__slots__` is its ability to reduce the wastage of space. By preventing the creation of a `__dict__` for each instance, which typically stores attribute names as strings and their corresponding values, `__slots__` leads to a substantial reduction in memory overhead. For classes that are instantiated many times, this can translate into significant memory savings.Don't forget about __slots__ in Python! | by AM For example, a class with several attributes defined in `__slots__` will occupy less memory per instance compared to an equivalent class without `__slots__`When should I use __slots__ in a Python class, and what .... This is particularly relevant when working with large datasets or in memory-constrained environments.

Speed Improvements

While not always as dramatic as memory savings, using `__slots__` can speed up the program by allocating space for a fixed amount of attributes. Because Python knows the exact attributes an instance will have, it can access them more directly. This eliminates the overhead associated with looking up attribute names in a dictionary__slots__ Usage : r/learnpython. This optimization is more pronounced in scenarios involving frequent attribute accessWhat Does Python's __slots__ Actually Do?.

Preventing Dynamic Attribute Creation

As mentioned, `__slots__` allows us to explicitly declare data members, which in turn means it prevents the creation of `__dict__`. This also means that Python no longer uses a `__dict__` to store attributes.2024年8月9日—Is it possible to access instance attributes defined in__slots__? Like you would access them by subscribing self.__dict__["attr"] in a dynamic class. Consequently, the ability to dynamically add arbitrary attributes to an instance after its creation is disabled. This can be beneficial for enforcing data integrity and predictability within your class structure.

When you use `__slots__`, Python does not create a `__dict__` for each object. Instead, it allocates a static structure (akin to a C struct) for the attributes defined in `__slots__`.

When and How to Use `__slots__`

The decision to use `__slots__` should be carefully considered. It is most beneficial for classes that are instantiated in large numbers, where memory consumption is a primary concern. Examples include data-holding classes, frequently used objects in loops, or when integrating with C-based extensions that expect a more memory-efficient structure.

To implement `__slots__`, you need to define a `__slots__` attribute on your class that points to a tuple of strings representing the valid attribute names.

```python

class Point:

__slots__ = ('x', 'y') # Define allowed attributes

def __init__(self, x, y):

self.x = x

self.Therefore,do not use __slots__ to retrieve the field names of a dataclass. Use fields() instead. To be able to determine inherited slots, base class __slots__ ...y = y

```

In this example, `x` and `y` are the only attributes that an instance of `Point` can have.

Important Considerations and Caveats

While powerful, `__slots__` comes with certain limitations and considerations:

* No `__dict__`: The most significant implication is the absence of the `__dict__` attribute. This means you cannot dynamically add new attributes to an instance after its creation.2021年3月14日—1 功能. __slots__是python类的魔法属性，可接收一个iterable对象作为属性。定义后，该类实例只能创建__slots__中声明的属性，否则报错。 If you need this flexibility, `__slots__` might not be the right choice. You also cannot use `vars()` on an instance of a class with `__slots__`.2024年8月28日—Enter slots, a feature that allows you to define a fixed set of attributes for your class, reducing memory overhead and potentially speeding up attribute ...

* Inheritance: When you define `__slots__` in a base class, child classes will inherit these slots.Python __slots__ If a subclass also defines its own `__slots__`, the instances of the subclass will have attributes from both the parent's and the subclass's `__slots__`.2023年11月3日—The fix is tospecify the slot variables as the private variables you want to use, instead of the properties you want to expose. If a child class does not define `__slots__`, it will have a `__dict__` in addition to the inherited slots. Do not use `__slots__` to retrieve the field names of a dataclass; use the `fields()` function instead.

* Class Variables: Defining `__slots__` can sometimes lead to unexpected behavior with class variables if not handled carefullyThey create a Python class who's name is the same as the enum typedef, and each member of the enumeration is defined as a member variable of the class.. The fix is often to specify the slot variables as the private variables you want to use, rather than the public properties you intend to expose directly.

* Weak References: Instances of classes with `__slots__` do not support weak references unless the `__weakref__` slot is explicitly included in `__slots__`.

* Multiple Inheritance with `__slots__`: While possible, multiple inheritance with classes that use `__slots__` can become complex and require careful management of attribute definitions across base classes.How and when to use __slots__ in python - Aabid Sofi

`__slots__